1. Field of the Invention
The present invention relates to an open/close member driving apparatus for opening and closing an open/close member which is supported on a vehicle body or the like in such a manner as to be opened and closed.
2. Description of the Related Art
Heretofore, open/close member driving apparatus includes an output drum and a clutch mechanism. The output drum is pivotally supported on a base member via a shaft in such a manner as to rotate freely and round an outer circumferential surface of which a cable which transmits a driving force to an open/close member such as a sliding door is wound. The clutch mechanism, into which a driving force from a motor is inputted via a speed reduction mechanism, is switched between an engaged state in which the driving force is transmitted to the output drum and a disengaged state in which the driving force is not so transmitted.
The clutch mechanism includes an annular field core into which an electromagnetic coil is incorporated and which is fixed to the base member, a rotor which is fitted rotatably on the shaft on which the output drum is pivotally supported and which can rotate by a driving force from the motor, and an armature which is supported in such a manner as to rotate and move axially relative to the shaft. The clutch mechanism is put in an engaged state by magnetically attracting the armature to the rotor when the electromagnetic coil is energized so as to transmit a rotation of the rotor to the output drum via the armature. Accordingly, the clutch mechanism thereby moves the open/close member to its open and closed positions via the transmission member (refer, for example, to JP-A-2005-232918 [FIGS. 4, 5]).
In the related open/close member driving apparatus that has been described above, power transmission between the armature and the output drum is enabled via a power transmission portion which is realized by bringing projections provided on an internal side of an end lid portion of the output drum into engagement with engagement holes provided in the armature. In addition, the position of the power transmission member is set in a substantially intermediate position between the shaft and an inner circumferential surface of the drum. Because of this, a rotational torque acting on the projections on the output drum becomes large, compared to a case where the power transmission portion is provided in a position lying close to the inner circumferential surface of the drum. Thus, countermeasures need to be taken such as those in which the projections on the output drum are made so thick as to bear a resulting high load or the output drum itself is formed of a relatively expensive, high-strength resin material. However, making the projections thicker has resulted in a problem that the overall size of the driving apparatus is enlarged, and forming the output drum of the high-strength resin material has resulted in a problem that the production costs are increased.